Anti-apartheid icon Nelson Mandela is spending a twelfth day in a South African hospital after being diagnosed with a lung infection and undergoing gallstone surgery.

South Africa's government has said the 94-year-old Mandela was admitted Dec. 8 to a hospital in the country's capital, Pretoria. Officials said Mandela underwent an endoscopic surgery to remove gallstones Saturday after doctors treated him for a recurrent lung infection.

On Tuesday, President Jacob Zuma said in a statement that Mandela required "extraordinary care" due to his age and could spend several more days in the hospital recovering.

Mandela is revered for being a leader of the struggle against racist white rule in South Africa, serving 27 years in prison for his beliefs. He served one five-year term as president before retiring from public life.